The actress and screenwriter goes behind the camera for a personal story inspired by her early years, featuring Ronan in what may be her finest work yet.

Greta Gerwig is no stranger to working both in front of and behind the camera, but her solo directorial debut “Lady Bird” will see her trying something new: not starring in her own material. Instead, two-time Oscar nominee Saoirse Ronan takes over as the star of Gerwig’s creation, leading the feature as the eponymous Lady Bird. Well, sort of.

The relationship comedy stars Ronan as Christine McPherson (Lady Bird, and no, no relationship with the wife of LBJ), a rebellious student at a conservative Catholic Sacramento high school who wants to escape her family and small town constraints to go to college in New York. The film is reportedly loosely based on Gerwig’s own experiences — the filmmaker and actress also grew up in Sacramento, where she attended Catholic school and set her sights on a life in New York City.

The film follows her acting and screenwriting collaborations with Noah Baumbach on “Frances Ha” and “Mistress America,” and co-directing “Nights and Weekends” with Joe Swanberg. Gerwig has already emerged as one her generation’s finest actors — her stirring and mostly underappreciated turn in “20th Century Women” most recently proved that to be true — with a real knack for writing both comedy and deeply human characters that pop right off the screen. “Lady Bird” is shaping up to be a continuation of her career, and a tremendous next step for the filmmaker.

“Lady Bird” earned acclaim at Telluride over the weekend and will next stop at the Toronto International Film Festival as the Opening Night selection for the Special Presentations section. A24 will release it this fall.